A grade crossing predictor (often referred to as a crossing predictor in the U.S., or a level crossing predictor in the U.K.) is an electronic device that is connected to the rails of a railroad track and is configured to detect the presence of an approaching train and determine its speed and distance from a crossing (i.e., a location at which the tracks cross a road, sidewalk or other surface used by moving objects). The grade crossing predictor will use this information to generate a constant warning time signal for controlling a crossing warning device. A crossing warning device is a device that warns of the approach of a train at a crossing, examples of which include crossing gate arms (e.g., the familiar black and white striped wooden arms often found at highway grade crossings to warn motorists of an approaching train), crossing lights (such as the red flashing lights often found at highway grade crossings in conjunction with the crossing gate arms discussed above), and/or crossing bells or other audio alarm devices. Grade crossing predictor are often (but not always) configured to activate the crossing warning device at a fixed time (e.g., 30 seconds) prior to an approaching train arriving at a crossing.
Typical grade crossing predictors include a transmitter that transmits a signal over a circuit formed by the track's rails and one or more termination shunts positioned at desired approach distances from the transmitter, a receiver that detects one or more resulting signal characteristics, and a logic circuit such as a microprocessor or hardwired logic that detects the presence of a train and determines its speed and distance from the crossing. The approach distance depends on the maximum allowable speed of a train, the desired warning time, and a safety factor. Preferred embodiments of grade crossing predictors generate and transmit a constant current AC signal on the track circuit; the predictor detects a train and determines its distance and speed by measuring impedance changes caused by the train's wheels and axles acting as a shunt across the rails, which effectively shortens the length (and hence lowers the impedance) of the rails in the circuit. Multiple grade crossing predictors can monitor a given track circuit if each predictor measures track impedance at a different frequency. Measurement frequencies are chosen such that they have a low probability of interfering with each other while also avoiding power line harmonics.
As is known in the art, there is a need to confirm that grade crossing predictors, as well as other railroad equipment, are operating properly to ensure public safety at railroad crossings. Troubleshooting a grade crossing predictor often involves connecting a laptop to the predictor and accessing diagnostics screens to see if system status outputs (e.g., electrical signals) indicate that the equipment is functioning correctly. Because the diagnostic screens only provide the end results of how the predictor is working with limited information about the inputs used to achieve the results, a maintainer must review reference manuals, installation diagrams, event diagrams and/or other materials to determine the cause of detected problems/anomalies.
As can be appreciated, this process requires a fair bit of experience and guess work on the part of the maintainer, since the underlying logic used to formulate the system outputs is not explained or visible. The maintainer will typically spend a great deal of time searching through the screens and paperwork to determine where an anomaly lies—this is undesirable as it wastes manpower and could cause the railroad equipment to remain in a sub-optimal operating state until the problem is fixed. Moreover, the process involves guess work, hunches and previous experience with the equipment, which is also undesirable.
Thus, there is a need and desire for a better troubleshooting technique for railroad equipment such as e.g., grade crossing predictors.